Safety critical
Safety critical means essential to safe performance or operation. A safety critical system, subsystem, component, condition, event, operation, process, or item is one whose proper recognition, control, performance, or tolerance is essential to ensuring public safety. Something that is safety critical item creates a safety hazard or provide protection from a safety hazard.
Source
14 CFR § 401.5
Scoping language
For the purposes of parts 415, 417, 431, 435, 440, and 460 of this chapter, the following definitions apply: